From Wikipedia:
Although Ford had taken great care to blend into Earth society, he had "skimped a bit on his preparatory research," and thought that the name "Ford Prefect" would be "nicely inconspicuous." Adams later clarified in an interview that Ford "had simply mistaken the dominant life form." The Ford Prefect was, in fact, a British car manufactured from 1938 to 1961
..... Nowadays, the joke is largely lost on younger audiences in Britain as well, since the Ford Prefect is now a rare sight on British roads.

....Prior art for Adams' satirical point – that humans attach such importance to their automobiles that a visiting extraterrestrial might reasonably mistake them for the planet's dominant life form – can be found in a widely reprinted article from The Rockefeller Institute Review titled Life on Earth (by a Martian) by Paul Weiss

My father actually clued me in on that one the first time I read HHGTTG, otherwise that would fly right over.

Im going to finish reading it tonight so I'll get "_____" to show the type of things I think are going over my head.... maybe Im just paranoid.